In the example disclosed in Patent Literature 1, a light source unit is made up by arranging semiconductor laser 1, an optical waveguide formed in element 2, and a plurality of lenses 3 and 4 for coupling a light flux emitted from the semiconductor laser 1 to the optical waveguide formed in the element 2, along optical axis 7 representing a straight line, as shown in FIG. 8.
To couple the light flux emitted from the semiconductor laser 1 to the optical waveguide formed in the element 2 successfully, each of the lenses 3 and 4 needs to be capable of being adjusted in terms of positions in directions 3a and 4a which are perpendicular to the optical axis 7. The direction 3a is perpendicular to the direction 4a. 
Therefore, lenses 3 and 4 are mounted on SIDM (Smooth Impact Drive Mechanism) (registered trademark) units 5 and 6 respectively, as shown in FIG. 9. The SIDM unit 5 is composed of movable portion 5a and of fixed portion 5b. In the same way, the SIDM unit 6 is composed of movable portion 6a and of fixed portion 6b. The movable portion 5a moves in direction 3a, and the movable portion 6a moves in direction 4a. Lens 3 is fixed on the movable portion 5a, and lens 4 is fixed on the movable portion 6a. 
In a light source unit having the aforesaid construction, dimension 7b in the direction of optical axis 7 is long, because the optical axis 7 is a straight line. Further, dimension 3b in the direction 3a perpendicular to the optical axis 7 grows greater when SIDM unit 5 is added, and dimension 4b in direction 4a which is another perpendicular direction to the optical axis 7 grows greater when SIDM unit 6 is added. Those enlarge the size of a casing in which the light source unit is housed.
The large-sized casing tends to be deformed largely due to temperature and to change relative positional relationship of members housed in the casing, which is not preferable.
When considering the casing to be incorporated in a product as a part, the large-sized casing tends to be avoided.
Patent Literature 1: JP-A No. 2005-222049